The invention resides in an Electron-Cyclotron-Resonance-Ion-Source (ECRIS) and a method for the operation of such an ECRIS and to vessel supports (stents) which have been doped with radioactive and non-radioactive atoms and molecules.
Such vessel supports, called stents in professional terminology, are used in the medicine in the treatment of vessel stenoses. For such treatment, struts are doped with a radioactive element whose half-life depends on the healing period for a surgical injury. Residual stenoses are to be prevented thereby.
Since the half-life is a relatively short periodxe2x80x9414 days is a reasonable periodxe2x80x94such stents cannot be stored. Rather, these stents must be doped quantitatively and in a reproducible manner with the suitable radioactive element, wherein the radioactivity remaining at the time of insertion into the human body, the transport distance and the transport time from the doping up to the implantation must be taken into consideration for the doping prescription.
There is therefore the question what the optimal irradiation procedure is and with what kind of apparatus such irradiation can be reliably and reproducibly performed.
Such an irradiation apparatus consists of three main components, that is, an ion source with a extraction system, a mass separation device in the form of a dipole magnet and an irradiation chamber. It is known that electron-cyclotron-resonance-ion sources provide a large amount of ion radiation of high quality. Such an ion source is therefore part of the apparatus. A mass separator is a dipole magnet which fans out, in a mass-specific manner, the extracted ion beam, while the beam passes through the mass separator passage. Finally, in the irradiation chamber, the object is subjected to the selected partial beam for doping. The insertion into and removal of the object or objects from, the irradiation chamber occurs by flushing the chamber with argon and then opening the chamber.
ECR ion sources are explained in, among others, the handbook xe2x80x9cIon Sourcesxe2x80x9d, published by Bernhard Wolf, 1995, CRC Press Boca Raton, New York, London, Tokyo. It provides an overview with hints to other sources. The basic ECRIS is described in this book among others in sections 9.2 xe2x80x9cWorking Principle of the Ion Source and Description of the Dischargexe2x80x9d on pages 122 to 127. The book xe2x80x9cElectron Cyclotron Resonance Ion Sources and ECR Plasmasxe2x80x9d by R. Geller, Institute of Physics Publishing, Bristol and Philadelphia, 1996 is more explicit and detailed. In this book, in addition to the chapter 2.4, Antennas and Coupling structures, the chapter 5 xe2x80x9cSimple Mirror . . . xe2x80x9d and 6, Min-B ECRIS for . . . xe2x80x9d are very explicit, particularly with respect to the source design.
ECR sources were first used mainly for the generation of highly charged ions for which microwaves of higher frequencies are needed. The use of lower frequencies still provides the advantage of a high ion yield, which is what is important here. Economically the use of lower microwave frequencies has the advantage that, for 2.45 GHz, reasonably priced microwave generators are available and furthermore only comparatively low magnetic fields are necessary. It is however difficult with these low frequencies to couple the microwaves to the plasma if the wavelengths are greater than the dimensions of the plasma chamber.
It is the object of the present invention to provide a reliable ECR ion source which exhibits a good long-term behavior so that one, or at the same time, more stents disposed in the irradiation chamber are subjected to a partial beam of constant quality from an ion beam which has been well fanned out mass-specifically in a reproducible manner for doping of the stents.
In an apparatus for the doping of vessel supports (stents) with radioactive and non-radioactive atoms comprising an electron-cyclotron-ion-source (ECRIS) with an arrangement for extracting an ion beam from the ECRIS, a magnetic separation device for the splitting of the ion beam arranged in a downstream area of the extracted ion beam and an irradiation chamber in which the vessel supports are exposed to the selected partial ion beam, the ECRIS includes a microwave-permeable plasma chamber with a magnetic, six-pole arrangement, an electrically conductive tube portion disposed within the plasma chamber co-axially with the six-pole arrangement and having an in-coupling opening and also being axially movable for an adjustment of an optimal in-coupling and a co-axial cable extends through the in-coupling opening and has an outer sleeve which is in electrical contact and an inner conductor which is electrically insulated and forms at the inner wall of the tube a flat loop whose end is in contact with the tube wall.
The six-pole magnet arrangement radially surrounding the plasma chamber is disposed in a dielectric tube and consequently insulates each of the solenoids which are disposed in the two end areas of the plasma chamber co-axially around the axis. This substantially improves the high voltage safety. Preferably, there is a foil in the tube, which has the advantage that no electrostatic field peaks can occur on the inner surface of the dielectric tube as they would occur with the sharp-edged structure of the six-pole arrangement without the use of the foil. Since the foil has no electrically conductive connection with the six-pole arrangement, it is charged at the edges by corona discharge so that the field strengths resulting in this discharge are partially compensated for whereby the corona discharge is again reduced.
The di-electric tube preferably consists of plexiglas, which is transparent and therefore facilitates a very good recognition of changes or damages as they may be caused by electrical stresses or thermal stresses.
The plasma chamber is preferably a (double-wall) Pyrex tube. In this way, the microwave energy can be coupled radially into the tube from all sides. The plexiglas has only a small recombination coefficient, which provides for a neutral gas share with a high hydrogen atom content. Hydrogen is chemically aggressive only in the atomic state (hydrogen nascendi) and reacts with phosphorus condensed on the wall to form gaseous phosphor hydrogen.
It is reasonable to operate the source continuously. A timed operationxe2x80x94which would basically be possiblexe2x80x94would be disadvantageous since, during the period in which the ion source is switched off, losses of radioactive phosphor hydrogen would still occur.
According to the basic process for operating the ECRIS, basically, the process should be maintained continuous. Masking out of a partial beam from the total beam depending on the gas and additional gas filling as well as the adjustment of the electrical operating parameters for the ECRIS and the separation magnet and of the exposure position of the stents should be, and is, possible, as will be explained later on the basis of FIG. 3.
An important electrical parameter is the adjustability of the high voltage of the ECRIS for the extraction.
The vessel support structure, that is the stent may be subjected to a partial beam selected from the ECRIS operated by the process.
The additional implantation of non-radioactive atoms changes the stents in an advantageous manner by preventing premature flushing during positioning of the stents and in their final positions.
The ECR ion source provides an ion beam of sufficient energy so that its useful part penetrates sufficiently deep into the stents. The energy is for example 60 keV. The microwave guiding requires no space beyond the space provided for the six pole arrangement. Another advantage of the apparatus is that additional ions for example suitable molecule ions are admixed to the beam provided by the separation magnet. They are implanted into the objects together with the radioactive and non-radioactive atoms, whereby the quality of the objects regarding corrosion and erosion of radioactivity is improved.
The invention will be described below in greater detail on the basis of the accompanying drawings. The drawings include FIGS. 1 to 3 and a table.